1. Technical Field.
This invention relates generally to switching circuitry for power and signal processing applications. More particularly, it concerns a one-cycle controlled switching circuit that renders the average value of the switched signal independent of disturbances. It also concerns a feedback control circuit that overcomes integrator reset problems in a way adaptable to constant frequency, constant ON-time, constant OFF-time, or variable switching circuits.
2. Background Information
U.S. patent application Ser. No. 752,068 filed Aug. 29, 1991 (the parent application) describes a one-cycle controlled switching circuit for power and signal processing applications. It effectively renders the output independent of disturbances such as input perturbations, load changes, and switching non-linearities. It does so by controlling the switch duty ratio for each cycle to significantly enhance switching circuit operation.
U.S. Pat. No. 4,862,057 to Contartese et al. also describes a switching circuit that controls the switch duty ratio. During each switch closure, the Contartese circuit multiplies the input voltage by the input current, integrates the product, extracts the square root, and then opens the switch when the square root exceeds a reference voltage. Doing so maintains the energy independent of input disturbances.
However, the Contartese circuit fails to render the chopped output signal independent of input perturbations and load changes because the output signal recovers only after many cycles. Further, the Contartese circuit does not produce a linear relation between the control reference signal and the switch output signal. The one-cycle switching circuit of this invention overcomes those drawbacks by integrating the chopped output signal y(t) during each switching cycle to produce a feedback signal v.sub.int indicative of the average value of the chopped signal during the cycle. Then, a comparator-and-switch-control circuit responds to the feedback signal v.sub.int and a reference signal v.sub.ref by varying the switch duty ratio as necessary to maintain the average value of the chopped signal at the indicated level during each cycle.
As a result, the average value of the chopped signal during any cycle is independent of disturbances. Input pertubations and load changes may affect the instantaneous value of the switch output signal during a cycle, but will not affect the average value because recover from a disturbance is completed in one cycle. Further, one-cycle control produces a linear relation between the control signal and the switch output signal. So, one-cycle feedback control based upon integration of the chopped output signal significantly enhances switching circuit operation.
In addition, the Contartese circuit integrates from the beginning of each cycle until the switching condition exists. It then resets the integrator to zero to await the beginning of the next cycle. In doing so, it does not maintain the energy constant in the discontinous current operation. Furthermore, resetting that way does not work with constant-on-time, constant-off-time, or variable switching circuits.
Recall that a constant-frequency switch is one in which the sum of the time the switch in the ON state and the time the switch is in the OFF state remains constant from one cycle to the next. So, integrating from the beginning of the ON state and resetting before the next cycle would appear to be a logical technique. A constant-on-time switch, however, is one in which the time the switch is in the ON state remains constant from one cycle to the next (i.e., the time it is in the OFF state is varied). A constant-off-time switch is one in which the time the switch is in the OFF state is constant from one cycle to the next (i.e, the time the switch is in the ON state is varied). A variable switch is one in which both the time the switch is in the ON state and the time it is in the OFF state may vary from one cycle to the next. Integrating from the beginning of the ON state and resetting to zero before the next cycle does not cause the average value of the chopped output signal to follow the control reference signal in each cycle for those switches. Thus, the one-cycle control technique described in the parent application needs feedback control circuitry that will work with all types of switches.